Black vine weevil was
brought to the US
on European nursery stock back in the mid-1800’s. This leaf-feeding insect is well
established now throughout the Flint,
MI area wherever yews are used as a landscape plant. These small insects are
rarely seen because they are nocturnal feeders, but the crescent-shaped gouges
left in the shrub leaves they feed on can easily be found. Black vine weevil feeding
damage on yew shrubs is sometimes hard to find as the dense foliage obscures
the notches, but on rhododendrons, holly shrubs, Japanese pieris, and euonymus
it is usually pretty easy to spot.
Although it is the notches
that black vine weevils create that attract our attention, it’s the larval
damage to the roots of plants that should be of most concern. Adult black vine
weevils emerge in the Flint
area in May and June and feed until fall.
The grubs, which are the larval form of black vine weevil, feed on shrub
roots and stems until the ground temperatures force them deeper into the soil
to hibernate.
Homeowners can take some
simple steps to reduce black vine weevil grub survival. Keep landscape mulch
from becoming too deep and don’t overwater your shrubs - especially in July and
August when the newly hatched grubs are most active. High soil moisture and over
mulching can lead to grub feeding on the stems of susceptible plants, and
girdled stems lead to extremely stressed or dead shrubs.
Spraying susceptible shrub
species, starting in the early summer, is effective at controlling adult black
vine weevil insects and limiting the amount of foliar damage to your shrubs. In
the Flint area
we start spraying for black vine weevil adults in June and recommend follow up
treatments in July and August.
The most common plants
attacked by black vine weevil are yew shrubs, rhododendron, holly shrubs,
Japanese pieris, or euonymus. If you have these shrub species in your landscape
you may want to have your plants checked for black vine weevil feeding damage.
